This invention relates to an apparatus for sealing a bore, a system comprising the apparatus and a method for using the apparatus. It relates, more particularly, to a sealing apparatus for use in a well pipe, the apparatus comprising a mandrel arranged around a centre axis through the apparatus; a radially movable gripping device arranged around the mandrel; a radially movable packer element arranged around the mandrel; and an axially movable activation device designed to set up axial forces for activating the apparatus. The invention also includes a method for using the apparatus in a well pipe.
Plugs may be used in, for example, the petroleum industry in a number of designs to isolate pressure areas and to seal pipes. This may be, for example, during operations in connection with the completion, maintenance and temporary or permanent closing down of a well.
From the publication U.S. Pat. No. 4,671,356 A, a sealing apparatus is known, including a plugging device, an anchoring device, and a centralizer. The plugging device and the centralizer are arranged around a pipe.
From the publication U.S. Pat. No. 3,912,006 A, an assembly of an anchoring device, a centralizer and a packer assembly is known. The anchoring device is configured to prevent axial movement when the packer assembly is being activated.
It can be challenging to ensure that the plug is in the desired position in a well pipe when it is being set in the well pipe; that it maintains its integrity and grip or attachment in the well pipe, that is to say it maintains its position in the well pipe; and possibly that it can easily be removed after use.
Especially in the case of larger pipe dimensions, the position of a plug in the well pipe may be of relatively great importance in how the plug attaches in the well pipe.
Should the plug sit with too large a centre deviation or directional deviation relative to the well pipe, the sealing of the plug may be unreliable. This is particularly relevant if there are large dimensional differences between the outer diameter of the plug and the inner diameter of the pipe, because the dimensional difference may lead to a skew orientation and thereby an unevenly activated packer element. This could also, as will be mentioned later, result in a failure to achieve sufficient anchoring to a pipe wall even though, on the surface, the right indications are received that the activation process which, in its turn, is to set the plug is running as normal.
Some plugs are designed in such a way that the gripping power against the well pipe is reduced if the tensioning of the plug is reduced in consequence of the packer element losing its axial tension. This may happen for example by thermally induced forces in a well and by various types of damage, for example damage from chemicals or mechanical damage.
It is obvious that a plug which has loosened and which is exposed to considerable pressure differences can cause much damage. At worst, the plug can come loose in consequence of high differential pressure from underneath relative to the orientation of the well towards the surface and further behave like a projectile and cause damage to mandatory safety components placed between the setting area of the plug and the access to the well pipe for running well equipment in.
It is also known that plugs may be difficult to remove. Some plugs are not designed to allow easy removal, whereas other plugs may have been exposed to incidents that have damaged setting and/or releasing mechanisms in such plugs. It happens that plugs have to be drilled out to be removable from the well pipe. Plugs that are made mainly from a composite material are known, but then with a limited range of application compared with the present invention.